The Refugee Action Coalition says detainees at the Nauru detention centre have gone on a hunger strike after a man tried to self-harm.

The Department of Immigration has confirmed 170 people are part of a peaceful protest and have begun to refuse food.

A department spokesman says the detainee was treated on site for superficial injuries.

Another man who claims to be a detainee on Nauru contacted the ABC about the incident.

The man, who gave his name as Mohammed, told the ABC's Laetitia Lemke that conditions on the island were unbearable.

"We didn't come to Australia because of food, because of clothes," he said.

"We were in danger in our country and we need a safe place.

"They sent us to a place that is worse than our country."

He says the detainees want to know why some asylum seekers are being sent to Nauru while others are detained on the mainland.

"What is different between those people - they pick up from one boat only 30 people to send here - the others [to] Darwin in [the] mainland. What is different?" he said.

He says the hunger strike will continue until the asylum seekers get answers.

"We had a peaceful protest before many times, but there is not any response from the government or any other organisation and we have to start the hunger protest from this morning to get any response from any organisation," he said.

He says everybody in the camp is on hunger strike and that the mental health of detainees is deteriorating.

"The thing is breaking under that strain and I think it's very clear that neither the camp, nor the Nauru government, has anything like sufficient facilities or services or resources to cope with what the Australian Government has dumped there now."

He says it is an increasingly volatile situation and the Government must start processing detainees' claims.

"They're constantly told the same thing - just wait, just wait, just wait," he said.

"You can't keep telling that to people. The uncertainty has created a huge mental health crisis in Nauru.

"As I said, we are looking at a very seriously deteriorating situation.

"The Government is sitting on a disaster that is not just waiting to happen, it's beginning to happen."

Returning home

﻿Meanwhile, the first Iraqi and Iranian nationals to voluntarily leave Nauru since the government began regional processing are on their way home.

The four Iraqis and two Iranians, all men, chose not to pursue asylum claims nor continue waiting in a regional processing centre in Nauru.

"Instead, they chose to return home voluntarily," an immigration spokesman said.